A man and a married woman meet at graduate school in 1950s America; the woman's husband transfers schools and she moves with him; it is 20 years before the two meet again. She is now a twice-divorced teacher and mother of three, he a married wealthy businessman. They become lovers. In 1981 she types up a contract declaring she will provide him with "mistress services" (all "housekeeping duties" and "sexual acts" he requests, the latter "with suspension of historical, emotional, psychological disclaimers for the duration of time requested") in return for "adequate accommodation and expenses accrued".

Despite its somewhat anachronistic terms, the arrangement has brought them happiness for 30 years – she is now 88 and he 93 and it's still in place. Shortly after the document was signed, she began to tape their conversations – the transcriptions of which became this book: candid discussions about marriage, inequality between the sexes, and feminism, by a couple intelligent enough to realise that their arrangement ensured they didn't spend enough time together to "warp each other by a series of compromises".

Already adapted into a stage play by Emmy-winning writer Abi Morgan, which will run at London's Royal Court theatre in the new year, the book offers a tantalising, no-holds-barred insight into the differences between the sexes, but it also hangs in that no man's land between actual, graspable memoir (the lack of specific biographical information about the authors can't help but leave a niggling doubt about its truthfulness) and theoretical tract.